Java Enumerations and Nested Classes

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Questions and Answers

What is an advantage of using enumerations in programming?

It provides more flexibility with dynamic values.
It is a data type that contains a fixed set of constants. (correct)
It is used for numeric or String constants.
It allows you to create an invalid enum value without a compiler error.

What is a characteristic of enum constants in an enumeration type?

They act like objects instantiated from the class. (correct)
They are only allowed for numeric or String constants.
They are static methods.
They are used for dynamic values.

What is the purpose of the compareTo() method in an enumeration type?

To check if two enumeration constants are equal.
To compare the ordinal of two enumeration constants. (correct)
To get the declaration order of an enumeration constant.
To create an invalid enum value.

What is an example of a situation where an enumeration would be useful?

When dealing with a fixed set of directions, such as compass directions. (C) Signup and view all the answers

How is an enumeration type declared?

Using the enum keyword. (A) Signup and view all the answers

What is true about the built-in methods of an enumeration type?

They are non-static and cannot be overridden. (A) Signup and view all the answers

Where can an enumerated type be declared in Java?

Only within a class (B) Signup and view all the answers

What is the purpose of the valueOf() method in the EnumDemo program?

To convert the user's input to an enumeration value (D) Signup and view all the answers

What is the data type of the pd variable in the main method?

Period (A) Signup and view all the answers

What is the purpose of the toUpperCase() method in the EnumDemo program?

To convert the user's input to uppercase (B) Signup and view all the answers

What is the purpose of the ordinal() method in the EnumDemo program?

To retrieve the position of the selected period in the enumeration list (C) Signup and view all the answers

What is the purpose of the Period.values() method in the EnumDemo program?

To retrieve an array of all enumeration values (B) Signup and view all the answers

What does the toString() method of an enumeration constant return?

The name of the calling constant object (C) Signup and view all the answers

What is the purpose of the ordinal() method of an enumeration constant?

To return an integer that represents the constant's position in the list of constants (C) Signup and view all the answers

What does the valueOf() method of an enumeration type do?

Returns the enumeration constant that matches the string parameter (C) Signup and view all the answers

What is the purpose of the compareTo() method of an enumeration constant?

To compare the constant with another constant (C) Signup and view all the answers

How can you declare a variable of an enumeration type?

By declaring a variable of the type and assigning a value (C) Signup and view all the answers

Where can you declare an enumerated type?

In a separate file with a.java extension (C) Signup and view all the answers

What is the position number of the grading period MIDTERM?

2 (C) Signup and view all the answers

What is the output of the program if the enum Size is PARTY?

799.00 (A) Signup and view all the answers

What is the main advantage of using enums in Java?

They make the values type-safe (B) Signup and view all the answers

What is the term used to describe a data type that allows only appropriate behaviors?

Type-safe (A) Signup and view all the answers

What is a class within another class called?

Nested class (B) Signup and view all the answers

How many types of nested classes are there in Java?

4 (D) Signup and view all the answers

What is the primary reason for nesting a class inside another?

To make the connection between the classes easier to understand and maintain (C) Signup and view all the answers

What is the HouseData class in the sample program?

A private inner class (B) Signup and view all the answers

What is the purpose of the RealEstateListing class in the sample program?

To describe the houses being sold by a real estate company (B) Signup and view all the answers

What is an anonymous class?

A special case of a local class that has no identifier (D) Signup and view all the answers

What is the purpose of the hData object in the sample program?

To store the address and area of a house (A) Signup and view all the answers

What is the benefit of packaging the classes together in the sample program?

It makes the connection between the classes easier to understand and maintain (C) Signup and view all the answers

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Study Notes

Enumerations

An enumeration (enum) is a data type that contains a fixed set of constants.
Enums are good to use when you already know all possibilities of the values or instances of the class.
Enums can be declared on their own or within another class.
Enums have built-in methods such as compareTo(), equals(), toString(), ordinal(), and valueOf().
compareTo() returns a negative integer if the calling object’s ordinal value is less than that of the argument, 0 if they are the same, and a positive integer if the calling object’s ordinal value is greater than that of the argument.
equals() returns true if its argument is equal to the calling object’s value.
toString() returns the name of the calling constant object.
ordinal() returns an integer that represents the constant’s position in the list of constants; the first position is 0.
valueOf() accepts a string parameter and returns an enumeration constant.

Creating Enums

To create an enum, declare a type with the enum keyword, an identifier for the type, and a list of values called enum constants.
An enumeration type such as Period is a class.
Its enum constants act like objects instantiated from the class, including having access to the methods of the class.
Enums can be declared on their own or within another class but not within a method.

Example of Enums

public enum Period { PRELIM, MIDTERM, PREFINAL, FINAL; }
Period is an enumeration type, and PRELIM, MIDTERM, PREFINAL, FINAL are enum constants.

Nested Classes

In Java, you can create a class within another class and store them together; such classes are called nested classes.
The containing class is the top-level class.
There are four types of nested classes: static member class, non-static member class (inner class), local class, and anonymous class.
The most common reason for nesting a class inside another is because the inner class is used only by the top-level class.

Example of Nested Classes

public class RealEstateListing { ... private class HouseData { ... } }
RealEstateListing is the top-level class, and HouseData is a private inner class.